My mom literally told me I’m her emotional trash can...

Update: I briefly mentioned my husband and daughter in the post, and I see comments telling me to move out... but both my sister and I are already married and moved out. My daughter is still too young to know what's going on, but my 3-year-old niece already says she hates her grandma because she's always screaming at grandpa. Since my brother-in-law, my husband, and the kids were all exposed to this, I couldn't hold it in any longer and finally snapped. A few years ago, my younger brother had a similar issue. He and Mom went to psychiatric counseling together, but Mom quit after saying she wasn't the one with the problem. She's basically estranged from my brother now. She also did couples counseling with Dad, but there was no progress. Yeah, Dad... Dad is definitely part of the problem. But at least he's someone you can talk to, and he had the will to improve. Grandma’s health only got really bad recently; I guess he couldn't bring himself to leave her in a nursing home while she was still okay. They had agreed on a senior center (daycare) where she'd go in the morning and come back at night, but I guess even that was too much for Mom. Anyway, the lack of communication between them is what led to this mess. Thanks to everyone who gave advice. I'm too hurt right now, so I'm going to distance myself from her. I'll wait and see, but if she continues to refuse treatment and stays like this, I'm going to cut ties for good.

I had a huge fight with Mom today. I think everything I’ve been bottling up just exploded. Whenever Mom gets stressed, she vents everything onto me and my sister. Mom has been looking after Grandma for over 10 years, but recently Grandma started showing dementia symptoms, so we moved her to a nursing home. That caused a lot of conflict with Grandma and Dad. We knew the situation was hard, so my sister and I tried our best to cater to Mom, but it got way out of hand. She acts like she’s the most miserable person in the world, blames everyone else for anything that goes wrong, and expects everyone to just take her tantrums. If you don’t agree with her, you’re suddenly the 'worst daughter ever.' It’s been getting worse every year for over a decade, and I feel like our whole relationship has become toxic. Mom started acting up again today, so I decided to give her some straight talk. She started wailing and screaming, making a scene because her daughter 'wouldn't take her side.' I told her to please just stop, that it’s too hard for us to keep walking on eggshells around her. I asked, 'Are we your emotional trash cans?' and she straight up said, 'Yes. You ARE my emotional trash cans.' She said since her husband and son don't understand her struggles, her daughters should be the ones to take it. She told me she regrets eating seaweed soup after giving birth to me (meaning she regrets having me) and called me a 'f*cking b*tch' and a 'crazy sl*t.' She even said I’d only get my head on straight when my own mother-in-law gets dementia and I have to slave away for her. She cursed at me some more, but I can't even remember it all... My sister, niece, husband, daughter, and dad were all right there. It was so shocking and humiliating. The moment I heard those words, I seriously thought about just cutting ties and never seeing her again. What should I even do? For context, the family basically dragged her to a psychiatrist before, and they told her she needs consistent treatment, but she only went a couple of times before quitting, saying nothing is wrong with her. Not just me, but the whole family is exhausted. If she actually gets psychiatric help, will things really get better?